In recent years, simultaneous multicomponent analyses using gas chromatograph mass spectrometers (GC-MS) or liquid chromatograph mass spectrometers (LC-MS) have been utilized in various areas, such as the testing of residual agricultural chemicals in foods, the testing of contaminants in environmental water, or the testing of drugs and poisons. For example, in a simultaneous multicomponent analysis for several hundred or even more compounds, it is often the case that there are a plurality of compounds which cannot be sufficiently separated in a GC or LC. In such a case, a tandem mass spectrometer, such as a triple quadrupole mass spectrometer or Q-TOF mass spectrometer, is often used as the mass spectrometer to minimize the influences of other compounds, unwanted foreign substances or other components which are eluted in a temporally overlapped form.
Normally, in a simultaneous multicomponent analysis using a GC-MS or LC-MS including a tandem mass spectrometer, a combination of the mass-to-charge ratio of a precursor ion and that of a product ion for a multiple reaction monitoring (MRM) measurement, i.e. an MRM transition, is set as the measurement target ions for each target compound. For each point in time at which one target compound is introduced into the mass spectrometer (retention time in GC or LC), an MRM measurement under the MRM transition corresponding to the compound concerned is performed, and the signal intensity of a product ion originating from the same compound is detected.
To obtain a correct result in such an analysis, an appropriate MRM transition needs to be set for each compound. Additionally, in the case of a triple quadrupole mass spectrometer or Q-TOF mass spectrometer, in which the precursor ion is fragmented by collision induced dissociation within a collision cell, the collision energy (CE) also needs to be appropriately set as one of the MRM measurement conditions, since the dissociation efficiency changes with the amount of collision energy imparted to the precursor ion.
For example, as disclosed in Non Patent Literature 1 or other documents, there is a conventionally known mass spectrometer which has the function of searching for an optimum MRM transition for a compound for which the MRM transition is unknown, and then automatically searching for an optimum level of collision energy for the optimum MRM transition. The use of such a function makes it possible to automatically search for an optimum MRM transition and optimum level of collision energy for each of a plurality of target compounds, and conveniently prepare a control sequence for obtaining necessary data for the quantitative determination of each compound in the sample based on the search result.
In the aforementioned automatic search for the MRM transition and collision energy, the MRM transition and collision energy are normally determined so as to achieve the highest detection sensitivity, i.e. to maximize the signal intensity obtained with a detector, for each compound. Searching for the level of collision energy which maximizes the signal intensity is common practice also in the case where an operator manually determines an optimum level of the collision energy, e.g. as described in Patent Literature 1, without using the automatic search.
However, in the case of the simultaneous multicomponent analysis mentioned earlier, it may be impossible to perform an appropriate measurement if an MRM transition and collision energy which have been determined so as to achieve the highest detection sensitivity for each individual compound are used. For example, in the testing of residual agricultural chemicals based on the “Positive List” (which is used in Japan to control foods containing residual agricultural chemicals), the measurement target concentration may significantly vary depending on the target compound, or the signal intensity may significantly vary depending on the target compound even when the component concentration in the sample is the same. In such a case, if the measurement conditions other than the MRM transition and collision energy are set so that a compound having a low signal intensity or low measurement target concentration will be detected with a sufficient level of sensitivity, the signal in the detector may become saturated for a compound which yields a high signal intensity or a compound which has a high measurement target concentration. Conversely, if the measurement conditions other than the MRM transition and collision energy are set so that a compound having a high signal intensity or low measurement target concentration will be detected with a sufficient level of sensitivity, the signal may become too low for a compound which yields a low intensity of signal or a compound which has a low measurement target concentration, making it impossible to accurately determine the quantity of the compound.
To avoid such a situation, in a conventional simultaneous multicomponent analysis, the large number of target compounds are divided into groups depending on the difference in their signal intensity or the difference in their measurement target concentration. Appropriate measurement conditions are set for each group, and the measurement is repeatedly performed, with the sample injected multiple times. However, a measurement divided into multiple times in this manner requires a correspondingly greater amount of sample. The consumption of the mobile phase used in a GC or LC (carrier gas for GC, or eluant for LC) also increases. Furthermore, the period of time for the measurement naturally increases, which lowers the throughput of the analysis as well as increases the operation cost.